PLANTS WITH TRAPS AND PITFALLS TO ENSNARE ANIMALS. 



121 



bifurcating, segments, or else only half of them are thus clothed with leaves whilst 

 the other half bear the before-mentioned bladders. The former is the case in 

 Utricularia minor, the plant represented in the background of the figure on p. 120; 

 and the latter in Utricularia Grafiana, which is drawn in the foreground. In 

 instances of the former kind obliquely ellipsoidal bladders are to be seen on short 

 stalks on the principal segments of the leaves, usually quite near their angles of 

 bifurcation. In the smaller species, such as Utricularia minor, they have a diameter 

 of about 2 mm. In individuals of the latter kind the bladders have longer stalks, 

 and are about 5 mm. in diameter. They are always pale-green and partially trans- 

 parent. Each bladder is somewhat flattened at the sides and exhibits a markedly 

 convex dorsal surface and slightly curved lateral surface. An orifice, whose border 

 is fringed with peculiar stiff" tapering bristles, leads into the interior of each of 

 these stalked bladders. The aperture has four rounded angles and is framed 

 as it were, by a 

 pair of lips. The 

 under lip is strong- 

 ly thickened, and 

 is furnished with a 



solid cushion projec- ^ /I 1 I \ \ ^l 



ting into the inte- / i \\ \ \\ 



rior of the bladder. 

 From the upper lip 



Fig. IS.— Traps nf Ut 



cglecla. 



Sa thin trans- i Ablacldermagnifled(x4). 2 Section of a bladder, s Absorption-cells on the internal 



surface of the bladder (x 250). 



parent, obliquely- 

 placed valve (see fig. 18^), the free edge of which rests upon the inner surface of 

 the cushion before referred to, and closes the entire orifice. This valve is very 

 elastic and yields easily to any pressure from outside. A tiny animal is able, by 

 pressing against it, to force a way without difficulty from the nether lip into the 

 interior of the bladder, and to slip in through the opening thus made. But as soon 

 as the animal has got inside, and ceases to press upon the valve, its elasticity brings 

 it back upon the under lip again. It cannot be opened by pressure from within; 

 for, resting as it does upon the projecting cushion, it is impossible for th^ little 

 prisoner to force it over the latter in an outward direction. 



The whole apparatus forms a trap for small aquatic animals, they being able, as 

 before observed, to slip into the bladder but not to get out again. Most animals 

 that enter make, it is true, eflEbrts to escape, but they are all in vain. Many perish 

 in a short time — about twenty-four hours — others live from two to three, or, in 

 some cases, even as much as six days. But in the end they must suffer death by 

 suffocation or starvation, and they then decay, and the products of their decomposi- 

 tion are sucked in by special absorption cells developed within the bladder. These 

 absorption cells (see fig. 18^) are linear-oblong and somewhat like little rods in 

 shape, and they line the whole internal surface of the cavity of the bladder. They 

 are arranged in fours, each group of four forming a cross and being united by a 



